Regenerative wave band filter



Feb. 10, 1942. J. STEINMETZ REGENERATIVE WAVE BAND FILTER Filed April 11, 1959 2 Sheets-Sheet l \...l Coup/mg 2 2% .9 la 7) J ,W l, 153%. 8 MI W.

Afforney Feb. 10, 1942 J. S-TEINMETZY 2,272,539

REGENERATIVE WAVE BAND FILTER Fild April 11, 1939 1 2 Sheets-Sheet 2 2 1 I k .1 Y

' "W r/lay I Patente'ireb. 1c, 1942 UNITED STAT Es PATENT OFFICE nEGE'NEnArIvE WAVE BAND FILTER Joachim Steinmetz, Berlin, Germany, assignor to C. Lorenz Aktiengesellschaft, Berlin-Tempelhof, Germany, a company of Ge rmany Application April 11.1939, Serial NI). 267,219 In Germany April 7, 1938 1 Claim. (01. 173-44) This invention relates to regenerative waveband filters, the band-width of which may be.

varied by changing the feedback.

It belongs to common technical knowledg that wave-band filters may be produced by introducing a counter-coupling, such as a negative fiers; As a matter of fact, the higher the amount of feedback is made in this type of amplifier, the wider is the amplified wave-band and, moreover, on exceeding the critical amount of coupling, the larger is the break-inattained in the band filter characteristic.

My invention consists of certain features of novelty which will be readily understood from the following description and be pointed out in the appended claim, reference being had to the accompanying drawings, in which the tubeand involves the advantage that the width of the band filter may be varied by means of a direct voltage regulation. However, the circuit arrangement shown in Fig. l suffers under the disadvantage that the inherent capacity of the resistance IR considerably'increases the;

anode-to-grid capacity of the tube, which increase in turn renders the filter characteristic curve strongly asymmetric. eflect involved by the anode-to-grid capacity might be slightly reduced by means of a seccndary coupling through aresistance R2 shown The deleterious;

. feedback, in high frequency double circuit ampliposite to that'described in connection with Fig.

1 so that an increased selectivity is obtained.

The deleterious eifect of the additional inherent capacity 'ofthe coupling resistance may be completely eliminated according to a further feature of my invention by circuit arrangements as illustrated in the Figs. 4 and 5, in which the regulation is effected by changing the feedback in the same manner as heretofore described, that is, either by varying the coupling resistance, or-

- by changing the slope of the tube characteristic in Fig. 2, but even this expedient has failed to provide the desired satisfactory results. a

It is proposed according to my invention tov overcome the heretofore .mentioned disadvantages by employing a circuit arrangement as shown in Fig. 3. arrangement is distinguished from that shown TinFig. 2 by an addi tionedcoupling 'coil L2 being closely coupled to an inductance coil forming part of the grid circuit of the tube. The effect thus obtained is that the feedback instead of ntroducing attenuation a cts'in a gain involving sense with the result that in response toa variable biasingpotential applied to the grid of this tube. Due to the fact that a'phase displacement of :90 degrees takes place in the wave-band filter, the impedance element I shown'in these figures must be purely capacitive or purely inductive inorder to attain a symmetric filter characteristic.- Dependent upon'the polarity of the inductance coils and whether the impedance element I is an inductance or acapacity, the feedback acts in an attenuating or in a gain involving sense.

The Figs, 6 to 9 show further circuit arrangements'representing further developments of my invention. The various couplings,

the arrangement of Fig. 6 positive feedback may be obtained through resistanceRz, and negative feedback may be obtained through impedances I and I or both feedbacks may be positive. Fig. I

7 shows an arrangement utilizing negative feedback through both-Rz and the impedances I and I. -The feedback through I and I may, ho'w ever, be positive. In Fig. 8 I have shown an arrangement for producing negative feedback through R2 and positiv feedback through impedances I and I. Fig. 9 illustrates a combination of the types of feedback shown' in Figs. 6-8 and in this case has negative feedback through resistances R2 and positive feedback through impedances -I and I. By simultaneously varying both feedback paths the band width may be maintained constant while the] filter characteristic is varied. It.is by no means necessary to concurrently use the entire number of coupling possibilities shown since the desired result will be obtained by employing any of the couplings indicated. Also in these embodiments of my invention'feedback may act in an attenuating or in a gain introducing sense, and the width of the wave-band may be increasedor -de-.

' creased dependent, upon the phase adjustment'of the feedback. Moreover, both kinds of feedback the width of the wave band decreases with higher feedback. The sense of regulation is thus opmay simultaneously-be used in each of the circuit arrangements referred to in the last paragraph,

Y whether ohmic or inductive, are indicated by arrows. In

band.

in which case a filter device is obtained in vvhich the wave-bard characteristic may be varied while main ining constant the width of the What is claimed is:

In a one/stage wave band filter having symmetric chai'acteristics, comprising a vacuum tube having an anode, a grid and a cathode, an input circuit having one terminal connected to said cathode, an inductance having one terminal connected to said cathode and the opposite terminal connected through a resistance to the opposite side of said input circuit. a second inductance l0 and the width'oi the wave band decreases as the ieedback is increased.

JOACHIM S'mmhrlETZ. 

